Highly pure ultra-fine SiOx powder and method for production thereof

ABSTRACT

A highly pure ultra-fine SiOx (wherein x is from 0.6 to 1.8) powder having a specific surface area of at least 10 m 2 /g and a total content of Na, Fe, Al and Cl of at most 10 ppm is provided. The SiOx powder is produced by reacting a monosilane gas with a gas capable of oxidizing the monosilane gas in a non-oxidizing gas atmosphere under a pressure of from 10 to 1000 kPa at a temperature of from 500 to 1000° C. In this case, the amount of the non-oxidizing gas is preferably larger than the total amount of the monosilane gas and oxygen participating in the oxidation of the gas capable of oxidizing the monosilane gas.

TECHNICAL FIELD

The present invention relates to a highly pure ultra-fine SiOx powder tobe used for an interlayer dielectric film of a semiconductor, a gasbarrier film, a protective film of an optical component, etc. and amethod for producing it.

BACKGROUND ART

A SiOx powder is used as a deposition material to form a deposited filmof SiOx on a food packaging film or an optical component because of itshigh vapor pressure. For example, it is used as a material to form a gasbarrier film comprising a SiOx film on a food packaging film to preventpermeation of water vapor or oxygen gas to prevent deterioration offood.

Conventionally, as a method for producing a SiOx powder, a methodwherein a mixed material containing silica and metal silicon and/orcarbon is subjected to a high temperature treatment in a non-nitridingatmosphere under at least 8×10⁴ Pa to form a SiO-containing gas, whichis cooled at a cooling rate of at most 1000° C./sec (JP-A-2001-158613),a method wherein a SiO₂ powder is heated in incomplete combustion flameto form Si vapor, which is suboxidized (JP-A-5-213606), etc., have beenknown.

In order to make the SiOx powder have a high purity in such conventionalmethods, it is necessary that impurities are not mixed during the timefrom preparation of a material to collection of a product. However, aspecial treatment such as purification is required to make the materialhave a high purity. Further, in order to generate SiO vapor or Si vaporby heating the material, a high temperature operation at from about 1500to about 2000° C. is required. In such a case, even if a high puritymaterial is employed, impurities such as Na, Al, Mg, Ca and Fe are mixedfrom e.g. the furnace material, and it is difficult to produce a highpurity SiOx powder.

DISCLOSURE OF THE INVENTION

Under these circumstances, it is an object of the present invention toprovide a highly pure ultra-fine SiOx powder. This object can beachieved by the present invention having the following gists.

-   (1) A highly pure ultra-fine SiOx powder, which is represented by    the formula SiOx wherein x is from 0.6 to 1.8, which has a specific    surface area of at least 10 m²/g, and which has a total content of    Na, Fe, Al and Cl of at most 10 ppm.-   (2) The SiOx powder according to (1), which is represented by the    formula SiOx wherein x is from 0.9 to 1.6.-   (3) The SiOx powder according to (1) or (2), wherein the specific    surface area is at least 50 m²/g and the total content of Na, Fe, Al    and Cl is at most 5 ppm.-   (4) A method for producing the highly pure ultra-fine SiOx powder as    defined in any one of (1) to (3), which comprises reacting a    monosilane gas with a gas capable of oxidizing the monosilane gas in    a non-oxidizing gas atmosphere under a pressure of from 10 to 1000    kPa at a temperature of from 500 to 1000° C.-   (5) The production method according to (4), wherein the amount of    the non-oxidizing gas is at least double the total amount of the    monosilane gas and oxygen participating in the oxidation of the gas    capable of oxidizing the monosilane gas by molar ratio.-   (6) The production method according to (4) or (5), wherein the gas    capable of oxidizing the monosilane gas is oxygen, air, NO₂, CO₂ or    H₂O.-   (7) The production method according to (4), (5) or (6), wherein the    non-oxidizing gas is argon or helium.-   (8) The production method according to any one of (4) to (7),    wherein the reaction is carried out in a non-oxidizing gas    atmosphere under a pressure of from 50 to 300 kPa at a temperature    of from 500 to 1000° C.-   (9) An interlayer dielectric film of a semiconductor device, a gas    barrier film of a solar battery, a gas barrier film of a food    packaging film or a protective film of an optical component, which    is formed from the SiOx powder as defined in any one of the    above (1) to (3).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: A schematic view illustrating a reaction apparatus employed inExamples of the present invention.

Explanation of numerical references 1 Reactor 2 Nichrome wire heater 3Oxidizing gas introduction pipe 4 Monosilane gas introduction pipe 5Discharge pipe

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be explained in further detail.According to the present invention, a reaction at a low temperaturebecomes possible by employing a monosilane gas as a material, and thusmixing of impurities from e.g. the furnace material as in a conventionalmethod can be decreased to the lowest level, and as a result, it becomespossible to make the SiOx powder to be formed have a high purity and beultra-fine.

In the present invention, as the monosilane (SiH₄) gas, a commerciallyavailable product may be used. The monosilane gas is superior to asilane type gas such as trichlorosilane from such a viewpoint that nochlorine is contained as a constituent. Further, as the gas capable ofoxidizing the monosilane gas (hereinafter referred to simply as“oxidizing gas”), in addition to oxygen gas and air, a gas having powerto oxidize the monosilane such as NO₂, CO₂ or H₂O may be used. It ispreferred that impurities in such an oxidizing gas are removed as far aspossible.

The reaction of the monosilane gas with the oxidizing gas is carried outin a non-oxidizing gas atmosphere under a pressure of from 10 to 1000kPa at a temperature of from 500 to 1000° C. If the pressure is lessthan 10 kPa, the formed SiOx film tends to be adhered and grow on thewall of a reactor, and block the discharge part, whereby long-termoperation is not easily carried out. Further, if it exceeds 1000 kPa,enormous installation tends to be required to increase the pressureresistance of a reaction apparatus, and further, impurities tend toincrease. The preferred pressure is from 50 to 300 kPa.

Further, if the temperature at the reaction site is less than 500° C.,SiO₂ is mainly formed, and if it exceeds 1000° C., Si tends to beformed, and further, impurities are more likely to be mixed from e.g.the furnace material, and production of a highly pure ultra-fine SiOxpowder becomes difficult in either case. The reaction temperature ispreferably from 550 to 950° C., particularly preferably from 650 to 850°C. The reaction time (the residual time of both monosilane gas andoxidizing gas in the reactor) is preferably from 0.2 to 1 second.

In the present invention, the reaction of the monosilane gas with theoxidizing gas is carried out in the presence of a non-oxidizing gas,whereby adhesion of the formed SiOx powder to the wall of the reactorcan be reduced. As the non-oxidizing gas, an inert gas such as argon orhelium is most suitable, however, H₂, N₂, NH₃, CO, etc. may be usedwithin a range of not impairing the reaction. In a case where air isused as the oxidizing gas, since the air contains N₂ and O₂, bothnon-oxidizing gas and oxidizing gas are used.

The amount of the non-oxidizing gas is preferably larger than the totalamount of the monosilane gas and oxygen participating in the oxidationof the oxidizing gas, and it is preferably at least double, particularlypreferably at least 10 times by molar ratio. Here, the amount of theoxygen participating in the oxidation of the oxidizing gas is, in a caseof the air for example, the amount of oxygen contained therein, in acase of NO₂ and CO₂, the amount of oxygen corresponding to one oxygenatom liberated therefrom, and in a case of H₂O, the amount of oxygencorresponding to the oxygen atoms constituting it.

As the reactor, use of one produced from a high purity material such asquartz glass is preferred. Its shape may be a cup form with bottom, buta tubular form is preferred, and its direction may be either vertical orhorizontal. As the heating method of the reactor, a resistance heatingelement, high frequency heating, infrared radiation heating, etc., maybe employed.

The SiOx powder formed in the reactor is discharged to the outside ofthe system together with the non-oxidizing gas and a by-product gas, andis recovered by a powder recovery apparatus such as a bag filter.

In the production method of the present invention, Siox powders havingvarious x values in SiOx are produced by changing the proportion of themonosilane gas to the oxidizing gas. If the x value of the SiOx powderof the present invention is outside the range of from 0.6 to 1.8, thedeposition rate decreases, and it is thereby necessary to increase thedeposition temperature, such being unfavorable. The x value ispreferably from 0.9 to 1.6. The x value can be obtained by measuring theSi molar amount in the SiOx powder in accordance with JIS-R6124(chemical analysis of silicon carbide abrasives) and measuring theoxygen molar amount by means of an O/N simultaneous analyzer (e.g.“TC-136” manufactured by LECO Corporation), to calculate the molarratio.

The specific surface area of the highly pure ultra-fine SiOx powder ofthe present invention is at least 10 m²/g. If the specific surface areais less than 10 m²/g, the deposition starting temperature tends to below. The specific surface area is preferably at least 50 m²/gparticularly preferably from 55 to 100 m²/g. Further, the total contentof Na, Fe, Al and Cl in the SiOx powder is at most 10 ppm. If the totalcontent of Na, Fe, Al and Cl exceeds 10 ppm, insulation failure orcorrosion may occur when the SiOx powder is used for an interlayerdielectric film or a negative pole active material of a lithium-ionbattery. The above total content is preferably at most 5 ppm,particularly preferably at most 3 ppm. These impurities may be measuredby means of emission spectrometry such as ICP. Further, of the SiOxpowder, the weight average particle size is preferably from 1 to 300 nm,particularly preferably from 1 to 50 nm.

The highly pure ultra-fine Siox powder of the present invention is usedas e.g. a deposition material to form an interlayer dielectric film of asemiconductor device, a gas barrier film of a solar battery, a gasbarrier film of a food packaging film or a protective film of an opticalcomponent.

EXAMPLES

Now, the present invention will be explained in further detail withreference to Examples and Comparative Examples.

Examples 1 to 13 and Comparative Examples 1 to 4

A monosilane gas, an argon gas and an oxygen gas (each having a purity≧99.999 mass %) were prepared, and each gas was introduced into areactor made of quartz glass (inner diameter 40 mm×length 800 mm)through a mass flowmeter. The monosilane gas was mixed with the argongas and supplied so that the mixed gas was blown into a low temperaturepart of the reactor 1 through a monosilane gas introduction pipe 4(inner diameter 5 mm) made of quartz glass. Further, the oxygen gas wassupplied to a high temperature part in the vicinity of the center partof the reactor through an oxidizing gas introduction pipe 3 (innerdiameter 5 mm) made of quartz glass so that the reaction took place atthe center part of the reactor (FIG. 1).

The reactor 1 was heated to maintain a predetermined reactiontemperature (Table 1) by turning on electricity through a nichrome wireheater 2 wound around the periphery of the reactor. The temperature wasadjusted by measuring the temperature by means of a thermocouple locatedat the center of the center part of the reactor and controlling theelectric power of the nichrome wire heater.

The pressure in the reactor was 100±10 kPa which is substantially thesame as the atmospheric pressure in many experiments. The pressurereduction less than the atmospheric pressure in the reactor was carriedout by adjusting the aperture of the valve while reducing the pressureby a vacuum pump located at the discharge side. Further, thepressurization exceeding the atmospheric pressure was carried out bycovering the reactor with a stainless container to make a doublestructure. In this case, a fibrous heat insulating material was embeddedbetween the nichrome wire heater and the stainless container, and at thesame time, an argon gas was introduced between the reactor and thestainless container so that the pressure was the same as the pressure inthe reactor so as to balance the gas pressures inside and outside thereactor.

The formed SiOx powder was discharged through a discharge pipe 5together with a by-product gas and the argon gas, and recovered by a bugfilter located on the way. Of the recovered powder, the x value of theSiOx powder, the specific surface area and impurities were measured. Theresults are shown in Table 1.

In Comparative Example 3 wherein the pressure in the reactor was 5 kPa,only a small amount of the product was recovered, and the most part wasadhered to the discharge part of the reactor. Further, the color tone ofthe recovered product was white, as contrasted with pale brown or liverbrown of products obtained in Examples. On the other hand, inComparative Example 4 wherein the pressure in the reactor was increasedto 1200 kPa, no desired specific surface area nor purity was obtained.

TABLE 1 Experiment conditions Re- Gas mixture Re- ac- Monosilane ratioExperiment results action tion gas system Oxidizing Gas Non- SpecificAmount of impurities temper- pres- Mono- gas system amount Mono- oxidiz-surface Total ature sure silane Argon Oxygen Argon Total silane/ ing gasx area Na Al Cl Fe amount ° C. kPa L/min L/min L/min L/min L/min oxygenratio *1 value m²/g ppm ppm ppm ppm ppm Comp. 427 103 0.16 15.84 0.402.00 18.40 0.40 32 1.9 80 1.2 0.5 0.8 1.1 3.6 Ex. 1 Ex. 1 527 103 0.1615.84 0.40 2.00 18.40 0.40 32 1.7 76 1.2 0.7 1.2 0.5 3.6 Ex. 2 627 1030.16 15.84 0.40 2.00 18.40 0.40 32 1.2 75 1.5 0.9 1.0 0.3 3.7 Ex. 3 727103 0.16 15.84 0.40 2.00 18.40 0.40 32 1.0 71 1.8 1.2 2.0 1.0 6.0 Ex. 4827 103 0.16 15.84 0.40 2.00 18.40 0.40 32 0.9 59 2.1 1.6 2.5 1.2 7.4Ex. 5 927 103 0.16 15.84 0.40 2.00 18.40 0.40 32 0.7 42 2.5 3.2 2.4 0.88.9 Comp. 1027 103 0.16 15.84 0.40 2.00 18.40 0.40 32 0.3 22 3.0 4.1 3.53.1 13.7 Ex. 2 Ex. 6 727 103 2.40 2.00 6.00 6.00 16.40 0.40 1.0 0.7 121.0 2.4 2.1 1.1 6.6 Ex. 7 727 103 0.38 11.50 0.96 4.80 17.64 0.40 12 0.818 0.9 1.8 1.9 0.8 5.4 Ex. 8 727 103 0.24 14.40 0.60 3.00 18.24 0.40 210.9 31 1.5 1.9 2.3 0.7 6.4 Ex. 9 727 103 0.11 11.10 0.28 7.00 18.49 0.3946 1.3 91 1.2 2.2 2.1 1.2 6.7 Ex. 10 727 103 0.16 15.84 0.20 2.00 18.200.80 50 0.6 62 0.8 1.6 1.8 1.1 5.3 Ex. 11 727 103 0.16 15.84 0.80 4.0020.80 0.20 21 1.6 38 1.4 1.2 2.2 0.9 5.7 Comp. 727 5 0.16 15.84 0.402.00 18.40 0.40 32 1.9 95 0.9 0.7 1.0 0.3 2.9 Ex. 3 Ex. 12 727 20 0.1615.84 0.40 2.00 18.40 0.40 32 1.4 74 1.5 1.6 1.2 0.7 5.0 Ex. 13 727 7000.16 15.84 0.40 2.00 18.40 0.40 32 0.8 15 2.1 2.4 2.1 1.0 7.6 Comp. 7271200 0.16 15.84 0.40 2.00 18.40 0.40 32 0.7 3 6.2 3.8 2.9 5.2 18.1 Ex. 4*1: Non-oxidizing gas ratio = (amount of argon gas)/{(amount ofmonosilane gas) + (amount of oxygen gas)}

It is found from Table 1 that the highly pure ultra-fine Siox (wherein xis from 0.6 to 1.8) of the present invention can be produced only by theproduction method of the present invention.

INDUSTRIAL APPLICABILITY

According to the present invention, a highly pure ultra-fine SiOx(wherein x is from 0.6 to 1.8) powder having a specific surface area ofat least 10 m²/g and a total content of Na, Fe, Al and Cl of at most 10ppm can be provided. The highly pure ultra-fine SiOx powder of thepresent invention can be used as a deposition material for production ofan interlayer dielectric film of a semiconductor, a plastic liquidcrystal panel, a gas barrier film of an amorphous solar battery, a gasbarrier film of a food packaging film, etc., or as a negative poleactive material of a lithium-ion battery. According to the productionmethod of the present invention, the above highly pure ultra-fine SiOxpowder can be easily produced.

1. A method for producing a powder represented by the formula SiO_(x)comprising: reacting monosilane gas, SiH₄,with a gas containing oxygencapable of oxidizing the monosilane gas in the presence of anon-oxidizing gas, under a pressure of from 10 to 1000 kPa at a hightemperature of from 500 to 1000° C. in a reaction zone to produceSiO_(x) powder, wherein x is from 0.6 to 1.8, the SiO_(x)powder has aspecific surface area of at least 10 m^(2/)g and a total content of Na,Fe, Al and Cl of at most 10 ppm, and the gas capable of oxidizing themonosilane gas is supplied to the reaction zone without prior mixingwith the monosilane gas, and the high temperature in the reaction zoneis obtained by heating the reaction zone on its periphery.
 2. The methodaccording to claim 1, wherein on a molar basis, the non-oxidizing gas isat least twice the total amount of the monosilane gas and oxygencontained in the gas capable of oxidizing the monosilane gas.
 3. Themethod according to claim 1, wherein the gas capable of oxidizing themonosilane gas is oxygen, air, NO₂, CO₂, or H₂O.
 4. The method accordingto claim 1, wherein the non-oxidizing gas is argon or helium.
 5. Themethod according to claim 1, wherein the pressure is from 50 to 300 kPaand the temperature is from 500 to 1000° C.
 6. The method according toclaim 1, wherein the reaction zone and gas introduction pipes are madeof quartz.
 7. The method according to claim 1, wherein the value of x inthe formula SiO_(x)is produced by changing the proportion of themonosilane gas to the oxidizing gas.
 8. The method according to claim 1,wherein the SiO_(x) powder is recovered by a powder recovery apparatus.9. The method according to claim 1, wherein the residual time of themonosilane gas and oxidizing gas in the reaction zone is from 0.2 to 1second.
 10. The method according to claim 1, wherein the reacting is ata temperature of 550 to 950° C.
 11. The method according to claim 1,wherein the reacting is at a temperature of 650 to 850° C.